Debt and Credit Facilities - Additional Information (Details) $ / shares in Units, shares in Millions			1 Months Ended				3 Months Ended		12 Months Ended
	Oct. 07, 2019 USD ($)	Sep. 05, 2019 USD ($) $ / shares shares	Aug. 31, 2019 USD ($)	May 31, 2019 USD ($)	Oct. 31, 2018 USD ($)	Feb. 28, 2018 USD ($)	Sep. 28, 2019 USD ($) $ / shares	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2015 USD ($)	Aug. 25, 2015
Line of Credit Facility [Line Items]
Long-term debt, gross									$ 5,132,000,000	$ 5,324,000,000
Gain from the extinguishment of long-term debt									(50,000,000)	0	$ 0
Long-term maturities during 2020									16,000,000
Long-term maturities during 2021									4,000,000
Long-term maturities during 2022									562,000,000
Long-term maturities during 2023									603,000,000
Long-term maturities during 2024									1,600,000,000
Commercial Paper
Line of Credit Facility [Line Items]
Maximum borrowing capacity									2,200,000,000
Long-term debt									$ 0
Average borrowing rate									2.54%
Revolving Credit Facility | Revolving Credit Facility 2017
Line of Credit Facility [Line Items]
Maximum borrowing capacity									$ 2,200,000,000
Borrowings outstanding									0
Letter of Credit | Revolving Credit Facility 2017
Line of Credit Facility [Line Items]
Maximum borrowing capacity									500,000,000
Fronting commitment sub-limit, maximum borrowing capacity									$ 450,000,000
Senior Notes | 4.6% senior notes due 2028
Line of Credit Facility [Line Items]
Debt instrument face principal amount					$ 700,000,000	$ 500,000,000
Debt instrument stated interest rate					4.60%	4.60%			4.60%
Proceeds from debt, net					$ 196,000,000	$ 497,000,000
Long-term debt, gross									$ 691,000,000	690,000,000
Proceeds from issuance of long-term debt					200,000,000
Senior Notes | 4.6% senior notes due 2029
Line of Credit Facility [Line Items]
Debt instrument face principal amount			$ 800,000,000	$ 650,000,000
Debt instrument stated interest rate			4.60%	4.60%					4.60%
Proceeds from debt, net			$ 159,000,000	$ 645,000,000
Long-term debt, gross									$ 804,000,000	$ 0
Repurchased face amount of debt				614,000,000
Repurchase amount				654,000,000
Contractual interest coupon and amortization of debt discount				3,000,000
Loss on repurchase of debt instrument				$ 43,000,000
Proceeds from issuance of long-term debt			$ 150,000,000
Senior Notes | 3.5% senior notes due 2021
Line of Credit Facility [Line Items]
Debt instrument stated interest rate			3.50%							3.50%
Long-term debt, gross									$ 0	$ 397,000,000
Repurchased face amount of debt			$ 150,000,000
Repurchase amount			155,000,000
Contractual interest coupon and amortization of debt discount			2,000,000
Loss on repurchase of debt instrument			$ 7,000,000
Senior Notes | 2.0% senior convertible notes due 2020
Line of Credit Facility [Line Items]
Debt instrument stated interest rate										2.00%
Senior Notes | 1.75% senior convertible notes due 2024
Line of Credit Facility [Line Items]
Debt instrument stated interest rate									1.75%
Convertible Debt | 2.0% senior convertible notes due 2020
Line of Credit Facility [Line Items]
Debt instrument face principal amount		$ 800,000,000										$ 1,000,000,000.0
Debt instrument stated interest rate												2.00%	2.00%
Long-term debt, gross									$ 0	$ 800,000,000
Repurchase amount					200,000,000		$ 200,000,000
Repayments of senior debt					$ 369,000,000
Convertible debt conversion ratio							0.0149186
Convertible debt conversion price (US$ per share) | $ / shares							$ 67.03
Repayments of debt	$ 600,000,000						$ 526,000,000
Debt conversion (in shares) | shares		5.5
Gain from the extinguishment of long-term debt							$ 4,000,000
Convertible Debt | 1.75% senior convertible notes due 2024
Line of Credit Facility [Line Items]
Debt instrument face principal amount		$ 1,000,000,000.0
Debt instrument stated interest rate		1.75%
Long-term debt, gross		$ 986,000,000							988,000,000	0
Convertible debt conversion ratio		0.0049140
Convertible debt conversion price (US$ per share) | $ / shares		$ 203.50
Conversion holding period		2 years
Discount rate		2.45%
Debt unamortized discount		$ 14,000,000
Repurchase of senior convertible notes		$ 14,000,000
Term loan | Term Loan due 2021
Line of Credit Facility [Line Items]
Long-term debt, gross								$ 400,000,000	$ 0	399,000,000
Weighted average interest rate, over time									3.68%
Line of Credit | Revolving Credit Facility | Revolving Credit Facility 2017
Line of Credit Facility [Line Items]
Proceeds from lines of credit								$ 400,000,000
Repayments of lines of credit										400,000,000
U.S. | Pension Benefit Plans
Line of Credit Facility [Line Items]
Defined benefit plan, contributions by employer						$ 500,000,000			$ 3,000,000	$ 503,000,000